In general, machines capable of locomotion can be divided between those which require interactive control by a human operator and those which are self-controlling to some degree. With the rapid innovations of recent years in computer technology, interest and design activity has increased in the development of self-controlled mobile machines, often called robots.
It is axiomatic that before a control system of a self-controlled mobile machine can precisely guide the machine through an environment having obstacles, the control system must be capable of ascertaining the position and velocity of the machine relative to the obstacles. In other words, the system must be able to respond to features of the terrain and environment in which the machine operates.
One technique devised to provide such a capability is to limit movement of the machine to an established environment containing reference points which are easily detected by the control system. For example, a mobile machine can be constrained by control wires embedded in the operating terrain which provide signals as the machine approaches and thereby establish artificial boundaries which limit the range of possible motion of the mobile machine. Similarly, the machine may be designed to track a wire embedded in the operating environment. Such a device is disclosed in U.S. Pat. No. 4,180,964. Mobile machine systems operating on both of these methods are well-known and in widespread use today.
Other prior art control techniques do not require an established environment containing "live" reference points. Instead, they provide a sensing means by which the control system can ascertain the position of the mobile machine relative to one or more fixed passive reference objects which are recognizable to the control system. Several prior art researchers have accomplished this using a camera and standard target. The premise underlying this approach is that the position of the mobile machine can be calculated from the apparent dimensional and parallactic changes in a target of known dimensions and geometry caused by movement of the sensing means mounted to the machine. For example, one such system uses a diamond shaped mark which has its diagonals oriented horizontally and vertically. With this method, a camera lens mounted to the mobile machine is maintained at the same elevation as the mark with the optical axis of the camera pointed at the center of the mark. The location of the camera and mobile machine is determined by trigonometric computations which relate the apparent size and geometry of the received image to the actual size and geometry of the known target.
Another approach uses a mark (a sphere with vertical and horizontal circles) which will directly produce at least one of three positional parameters which relate the target location to the camera location (i.e. distance, elevation and azimuth angle). The geometry of this mark is such that the mark's shape remains unchanged when its center is viewed along the optical axis of the camera.
The prior art techniques described above have several limitations. The defined environment techniques require the installation of expensive, energy consuming beacons which require rotational scanning or the like. These techniques also may be limited by the physical terrain (e.g. corners or hills). The techniques using a reference mark require the receiving camera lens to remain focused on the mark at all times or to scan the environment. Furthermore, these techniques may require that the camera and reference mark remain at the same elevation. It is an object of the present invention to provide a sensory apparatus which avoids these limitations.